It is often desirable or necessary to provide a position feedback signal for an actuator device which is utilized to produce motion or positioning of a component of a machine or other equipment. Such instances occur in the design of industrial equipment and such machinery as earth moving and farm equipment for the control of implements such as backhoes, buckets, bulldozer blades, plow blades, etc.
Such feedback signals are desirably electrical and are generated by an electrical transducer associated with the movable part or with the part actuator member, which causes positioning of a transducer element such as to create electrical output signals corresponding to the position of the movable part. These transducers have often taken the form of slidewire or potentiometer devices having either linear or rotary elements which are drivingly connected to the movable elements to provide this transducing function.
The actuator is typically comprised of a fluid pressure actuator and commonly takes the form of a pneumatic or hydraulic power cylinder with a piston reciprocated in a cylinder by the application of fluid pressure. The piston motion is transmitted to the controlled component via a suitable driving connection to cause the movement or positioning of the controlled part or component.
Often, the transducer is mounted in a relatively vulnerable position and is of relatively fragile construction such as to be subject to malfunction due to mechanical abuse and/or environmental conditions such as the presence of dust, dirt or other contaminants.
This is particularly a problem in application to earth moving and farm equipment.
There have been a number of prior attempts to provide a direct association of the transducer with the fluid actuator in order to have a self-contained fluid actuator feedback transducer. Typical of these approaches are those disclosed in U.S. Pat. Nos. 3,915,070 to Mailliet; 4,121,504 to Nowak; 4,179,982 to Saotome and German Pat. No. 2,339,324 to Jurgen Lohse. In these prior art approaches, either a linear or rotary motion is imparted to a detector element, associated with the piston and cylinder to produce a corresponding output motion. This element is coupled to a transducer to produce an electrical output signal.
However, in these instances, the transducer is mounted externally of the cylinder and also is driven with relatively elaborate driving connections between the movable element and the transducer such that the resultant combination is relatively costly, severely limiting the application of such devices and also remains vulnerable precluding use for the heavy service applications described.
In U.S. Pat. No. 3,403,365 to Richards, there is disclosed an attempt to protect the transducer by a more or less internal mounting of the transducer components. However, this arrangement requires the entire transducing assembly to be mounted within the interior of the piston rod, rendering such approach impractical for any but large size cylinders. Additionally, the particular mechanism is relatively complex and costly to manufacture.
Accordingly, it is an object of the present invention to provide an indicator arrangement for fluid pressure actuators of the piston and cylinder type which is readily adaptable for cylinders of all sizes.
It is yet another object of the present invention to provide such position indicator apparatus which is completely enclosed so as to be protected enabling use of such cylinders in rugged environments such as in agricultural and earth moving equipment.
It is still another object of the present invention to provide such position indicator for fluid pressure actuators which is extremely simple in configuration such as to be enabled to be provided at extremely low cost allowing such cylinders to be utilized in a great variety of applications.